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B4 (Photosythesis (Photosynthesis experiment... an example of a common…
B4
Photosythesis
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Green plants absorb light energy using chlorophyll in their leaves. They use it to react carbon dioxide with water to make a sugar called glucose. The glucose is used in respiration, or converted into starch and stored. Oxygen is produced as a by-product.
Photosynthesis takes place inside plant cells in chloroplasts. Chloroplasts (mostly found in the mesophyll layer) contain a green substance called chlorophyll.
Chlorophyll gives leaves their green color and absorbs light that is used in photosynthesis. Chlorophyll is found in high concentrations in chloroplasts of plant cells
Light converts Carbon Dioxide and Water into carbohydrates. Light energy is absorbed by chlorophyll while air containing carbon dioxide and oxygen enters the plant through the leaf stomata.
Photosynthesis experiment... an example of a common experiment used to investigate light intensity and the rate of photosynthesis is the pond weed experiment.
Set up the apparatus as in the diagram.
Leave for five minutes for the pondweed to acclimatise to the new light intensity.
Count the number of bubbles given off in one minute.
Move the light 10 cm further back.
Leave for five minutes for the pondweed to acclimatise again.
Count the number of bubbles given off in one minute.
Repeat by moving the lamp away by 10 cm intervals until 50 cm is reached.
Independent variable - the light intensity (how close the light is).
Dependant variable - the number of oxygen bubbles given off (the rate of photosynthesis).
Controlled variables - the size of the pond weed, the volume of water used and its temperature.
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Glucose
Storage
Glucose is needed by cells for respiration. However, it is not produced at night when it is too dark for photosynthesis to happen. Plants and algae store glucose as insoluble products. These include:
Starch
Fats and oils
Use
Some glucose is used for respiration to release energy. Some is used to produce:
Cellulose - which strengthens the cell wall
Proteins - such as enzymes and chlorophyll
Plants also need nitrates to make proteins. These are absorbed from the soil as nitrate ions.
To test leaves for starch you will need to...
heat a plant leaf in boiling water for 30 seconds (this stops its chemical reactions)
heat it in boiling ethanol for a few minutes (this removes most of its colour)
wash with water and spread onto a white tile.
add iodine solution from a dropping pipette.
If positive for starch blue/black colours will develop
The glucose made in photosynthesis is transported around the plant as soluble sugars. Glucose is used in respiration to release energy for use by the plant's cells. However, glucose is converted into insoluble substances for storage. These insoluble storage substances include:
Oils
Fats
Starch
While most of the energy stored in the body is stored as fat, glucose is so important to normal function that the liver and muscle cells store a certain amount of it for times during which blood glucose levels begin to run low.
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Anaerobic Respiration
Not enough oxygen may reach the muscles during exercise. When this happens, they use anaerobic respiration to obtain energy.
Anaerobic respiration involves the incomplete breakdown of glucose. It releases around 5% of the energy released by aerobic respiration, per molecule of glucose. The waste product is lactic acid rather than carbon dioxide and water:
glucose → lactic acid (+ little energy)
Muscle Fatigue: Muscles become tired in long periods of activity. Muscles stop contracting efficiently. One cause of lactic acid build up is the lack of oxygen supplied to the muscles. To remove the lactic acid the blood needs to flow through the muscles.
Fitness versus health: Fit people are able to carry out physical activities more effectively than unfit people. Their pulse rate is likely to return to normal more quickly after exercise.
Oxygen debt: Much less energy is released during anaerobic respiration than during aerobic respiration. This is because the breakdown of glucose is incomplete.
Anaerobic respiration produces an oxygen debt. This is the amount of oxygen needed to oxidise lactic acid to carbon dioxide and water. The existence of an oxygen debt explains why we continue to breathe deeply and quickly for a while after exercise.
Metabolism - Chemical processes inside of organisms that are necessary to maintain life, or how quickly you burn calories or fat.
Factors that affect metabolism are...
Muscle mass - The amount of muscle tissue on your body. Muscle requires more energy to function than fat. So the more muscle tissue you carry, the more energy your body needs just to exist.
Age - As you get older, your metabolic rate generally slows. This is partly because of a loss of muscle tissue, and also because of hormonal and neurological changes.
Genetics - This can also play a role in whether you have a slower or faster metabolism, and some genetic disorders can also affect your metabolism.
Physical activity - Regular exercise increases muscle mass and encourages your body to burn kilo joules at a faster rate, even when at rest.
Aerobic Respiration
Aerobic Respiration is the respiration in which requires the use of oxygen.
glucose + oxygen → carbon dioxide + water (+ energy) Glucose and oxygen are used up
Carbon dioxide and water are produced as waste products
Most of the reactions involved happen inside mitochondria, tiny objects inside the cytoplasm of the cell. The reactions are controlled by enzymes.
During exercise, the muscle cells respire more than they do at rest. This means that:
Oxygen and glucose must be delivered to them more quickly
Waste carbon dioxide must be removed more quickly
The increased heart rate increases the rate of blood flow around the body. The increased rate and depth of breathing increases the rate of gaseous exchange in the lungs.
The muscles store glucose as glycogen. This can then be converted back to glucose for use during exercise.
Plants store glucose as starch and animals store it as glycogen. In addition, respiration and breathing are not the same thing: respiration releases energy, while breathing lets air into and out of our lungs.
